In the past, a composite in which a carbon-based substrate and a silicon substrate are joined via an amorphous-silicon or silicon-carbide layer between their joining surfaces has been reported (Japanese Patent No. 4182323, Publication).
In the above structure, the joining surfaces are molten, thereby forming a layer of a compound of silicon and carbon. This method is advantageous in preparing a large-sized composite substrate.
It has been reported that, in cases where black lead is used for a substrate, a SiC layer is formed on the surface of the black-lead substrate in advance and an amorphous silicon layer is formed on the surface of the silicon substrate in advance, and then, the SiC layer and the amorphous silicon layer are joined, thereby preparing a composite thereof.
Moreover, as an example of a composite of a carbon-based substrate and a ceramic substrate, a composite obtained by joining a graphite film and a silicon substrate has been reported (JP-A-2008-294110). This patent literature has reported that the composite was obtained in the following way: after hydroxyl groups are formed on the surface of the graphite film and silanol groups are formed on the surface of the silicon substrate, both of the substrates are heated while pressure is applied on them, to cause silicon-carbide bonds, thereby joining the substrates.
Furthermore, there is a report in which a substrate that is obtained by forming a silicon oxide film through thermal oxidation of a silicon surface, and a graphite film with hydroxyl groups formed on its surface were subjected to a heat treatment while directly being applied with pressure, thereby producing a composite.
In this method, it is also reported that silicon-carbide bonds can easily be caused to join both the substrates.
The composites of graphite films and silicon substrates prepared by these methods are characterized in that the films and the substrates are joined via silicon-carbide bonds. As an example of a rigid composite in which SiC is formed in a joint interface between a carbon material and a ceramic or metal material, the composite disclosed in JP-B-58-6712 can be mentioned. Meanwhile, a composite that is obtained by joining ceramic substrates with a diffusion layer of oxygen, nitrogen or carbon and a metal layer included therein has also been reported (Japanese Patent No. 3505212, Publication).